1. Field of the Invention
The invention relates to a method of protecting heat-labile and/or oxygen-labile compounds and, more specifically, to heat- and/or oxygen-labile compounds that are coated to protect the activity of the compounds or the labile component of a food or feedstuff, particularly following extrusion, without sacrificing the bioavailability of the compounds upon ingestion.
2. Background of the Art
Many biologically important compounds lose activity if exposed to heat or oxygen, wherein the heat or oxygen lability of the compounds may be related to the degree of unsaturation, i.e., the presence of double bonds, of the compounds. Such compounds include many of the vitamins. Also included are antioxidants. Numerous attempts have been made in an effort to stabilize these compounds so that the activity of the compounds is maintained over longer periods of time upon exposure to heat and/or oxygen. Certain of these methods have focused on coating of the compounds with a protective material, including gelatin and alginate. Protecting the compounds against degradation is not the only concern, however. The protected compounds must also be available for biological absorption upon ingestion. These two purposes are inherently conflicting in that known methods of protection of the compounds during processing and storage have also limited or prevented absorption of the compounds so that less of the biologically important compound is effectively delivered to the ingesting organism.
One of the major uses of these heat- and/or oxygen-labile compounds is in the supplementation of food, including both human food and animal feed. Ambient temperatures and storage conditions typically lead to a loss of activity of the compounds over time frames that are usually shorter than the other limiting times for most foods. While the use of sealed containers and low-temperature storage ameliorates the degradation of the compounds, these methods are expensive and often not practical. Many food processing methods use heat which further reduces the level of active heat-labile and oxygen-labile compounds. A particularly common and destructive food processing method is extrusion, a process that involves aggressive comminuting of the food product under extreme temperatures and pressures. Extrusion is used in the commercial production of almost all dry pet foods, and is very common in the production of ready-to-eat cereals. Recent studies have shown in excess of 60% sacrifice of carotenoids through extrusion processing. Addition of the compounds after extrusion leaves the compounds more susceptible to oxidation due to oxygen in the atmosphere and results in visual detection of the compound on the surface of the food product. Application is also difficult because of product wicking of the surface of the extruded diet which results in active ingredients being transferred to the sides of the container in which the diet is stored.
Attempts to encapsulate biologically active compounds using gelatin have had mixed results. To be an effective coating, the gelatin must be extensively cross-linked. Unfortunately, cross-linked gelatin is not readily dissolved in the digestive tract. Accordingly, while increasing the cross-linking of the gelatin increases its protective qualities, it decreases the bioavailability of the protected compound. Various forms of alginate have been used in a variety of encapsulation techniques. One such technique involves dissolving sodium alginate in water, adding the "payload" compound to be protected, and spraying the solution into a bath containing calcium ions. As the droplets enter the bath, the soluble sodium alginate is rapidly converted into insoluble calcium alginate, effectively encapsulating the "payload" compound. The calcium alginate beadlets are digested by ionic exchange with other salts during digestion. However, the use of calcium alginate alone produces a beadlet that is substantially oxygen permeable. Tests on calcium alginate by Southwest Research Institute are that oxygen permeability of a calcium alginate membrane at standard temperature and pressure is 2.91.times.10.sup.11 cm cm.sup.3 /cm.sup.2 s (cm Hg).
The only option in the known prior art is to over-formulate the liable components that are included in the food or feedstuff. This over-formulation adds unnecessary expense and does not guarantee product performance. Neither alginate or gelatin beadlets have provided both adequate protection and bioavailability of the encapsulated compounds.
Encapsulation of the active compounds protects them against oxygen degradation not only through physical protection from contact with oxygen, but also by protecting them against interaction with oxidizing agents and free-radical initiators that may be present in the substrate, such as a food product, to which the encapsulated compounds have been added. For example, polyvalent metal ions, such as iron, copper, manganese, and chromium, are active oxidizing agents and are also present in food products, particularly food products that have been supplemented with such minerals for improved nutritional characteristics. The presence of these oxidizing agents ordinarily accelerates the oxygen degradation of the unprotected active compounds, particularly if elevated temperatures or pressures are present. In a similar fashion, encapsulation of the active compounds will protect them from radical initiators. In this regard, encapsulation of the active compounds serves another purpose. Certain of these active compounds, such as lutein, are not oxidizing agents or free-radical initiators themselves, but upon degradation become oxidizing agents or free-radical initiators.
Alternatively to coating the labile compounds, or supplementary thereto, is the process of coating of the known oxidizing agents or free-radical initiators that may be added to the product containing the labile compounds. For example, if polyvalent metals are to be added to a food product containing labile compounds, coating of the metals by the process of the present invention will serve to limit the degenerative effect that such substances may have on the labile compounds. In this way, the process of the present invention may be used either directly to protect the labile compounds themselves or indirectly by limiting the activity of oxidizing agents and free-radical initiators. In practical application, the compounds, either the labile compounds or the oxidizing agents or free-radical initiators, or both, being added to the product are subject to coating to provide the protective effect.
There is a need for a method for encapsulating heat- and/or oxygen-labile compounds, or oxidizing agents and free-radical initiators, or both, that will effectively protect labile compounds that have been added or that may otherwise be present from degradation and loss of activity, particularly through the extremely harsh extrusion process, while maintaining the bioavailability of the labile compounds upon ingestion after extrusion.